Hydrogen fluoride alkylation with effluent refrigeration



March 28, 1961 D. H. PUTNEY HYDROGEN FLUORIDE ALKYLATION WITH EFFLUENTREFRIGERATION Filed March 50, 1959 States Patent NO F HYDROGEN FLUORIDEALKYLA'HON Y EFFLUENT REFRIGErATIoN Filed Mar. 30, y179159,1Ser. No.802,908 2 Claims. (Cl. 2604683.48)

This invention relates to the :alkylationof isoparatlinic hydrocarbonswith olenic hydrocarbons and refersmore particularly to such analkylation process `wherein catalyst employed is hydrogen iluoride. l

vThis application is a continuation-impart of my copending application,Serial No. 565,081, led February 13, 19,56, entitled Hydrogen FluorideAlkylation With Eliiuent Refrigeration. April 10, 1959.

It is conventional in the art of hydrogen uoiide catalyzed alkylation tomix the catalyst and the hydrocarbons tobe alkylated in a reaction stepand then pass from the Y'reaction step `to an acid settling stage fromwhich is taken a hydrocarbon phase eiuent usuallyconi tainingapproximately 0.5 to 1.5 percent by 'weight of Ythe hydrogen fluoridecatalyst. The history of this art `discloses three alternative methodsof handling such hydrocarbon phase eflluent containing residual hydrogenliuoride. In one modification of the process, the hydrocarbon phaseeiuent was passed directly from the acid settling stage or stages to aneutralization tower to neu tralizev the yhydrogen liuoride. From theneutralization tower, the neutralized effluent was passed to the ldeisobutanizer tower. This variation of the process, however, wasobjectionable Ibecause there was too much residual acid to neutralizeinthe hydrocarbon phase.'

y'In a second variation, the hydrocarbon phase effluent from the acidsettling stage was passed directly t o the deisobutanizer, the overheadcontaining most' of theHF beingreturned to the reactor and the bottomsonly being sent to neutralization. This proved to be excessively hard onthe deisobutanizer tower, because the HF in the overl head being morethan the saturation'quantitywas largely yfree HF andvery corrosive.Finally, in a commonconventional variation of the process', the hydrogen`uoride containing hydrocarbon phase effluent is passed from the acidsettling stageV to an alloy Vstripper Ifrom thence' to thedeisobutanzer. This process provides the advantageous condition of nofree hydrogen fluoride in the deisobutanizer .at the cost ofprovidingthe expensive alloy stripper.

Additionally, `none of the -three variations of hydrogen fluoridealkylation was able to'achieve the advantages of'etlluent refrigerationof the reaction step as setA forth relative sulfuricl acid alklation inthe Putney Patent 2,664,452, issued vDecember 29,v 1953; Serial No;450,192, now U.S. Patent No. 2,949,494, David H. Putney, tiled August16, 1954, Alkylation of Hydrocarbons Utilizing Evaporative Cooling; andSerial N o. 565,090, David H. Putney, vtiled February 13, v19,56,Efiuent Refrigeration and now abandoned. Therefore, an object of theinvention is toprovide an alkyl'a'tion system catalyzed by hydrogenfluoride wherein the lalloy stripper is eliminated from the system yetno free hydrogen fluoride is present in the hydrocarbon plriaselefliuent passed to the deisobutanizer.

ICC

, Y2 quires no alloy stripper and yet passes substantially fhy'- vdrogen`iiuoride free hydrocarbon phase etiiuerittoV the `cleisobutanizerwhile, additionally, achieving the 'benefits of eiuent refrigeration forthe alkylation system,

Another object of the invention is to provide an alkylation systemcatalyzed 'by hydrogen fluoride wherein the hydrogen fluoride isseparated from the hydrocarbon phase effluent at low non-corrosivetemperatures without passing through `an alloy stripper, the hydrogenliuoride so removed recycled to the reaction st ep as a feedconstituentwithout damaging any equipment in the alkylation system. l Y

Other land further objects of the invention will appear in the course ofVthe following description thereof.

In the accompanying drawing ywhich forms a part of the specification andis to be read in conjunction therethe This application abandoned with, aschematic flow diagram of one embodimentv of the invention is shown.

Rewcton and acid settling Referring to the drawings, at 1 is shown theshell of a reactor equipped with an open-ended circulating tube 2. Atone end of the circulating tube is an impeller 3 which serves thepurpose of a circulating pump in cooperation with the circulating tube.Within the circulating tube 2 are a Vplurality of heat exchangerelements 4 comprising a tube bundle provided with a distributing head 5enclos.- ing one end of the reactor. The impeller 3 is mounted on ashaft 6 rotated through a reduction gear '7 by any suitable source ofpower or prime mover such Ias an elec,- trical motor or stream turbineVdiagrarnrnatically shown at 8. c

Circulation within the reactor is established by the impeller throughthe annular yspace between the shell V1 and `circulating tube 2 aroundthe cooling or kheat exe change tubes 4 and lback to the impeller. Thereaction can `also be accomplished in a vessel without heat eXf changeelements with the heat exchange step in a subsequent operation, orin avessel without internal circula'- tion. Olenic hydrocarbons andisobutane in excess are introduced to the system through lines 9 and 10,respeo` tively, andare combined in feed pipe .'11 priorto passage cycleacid is returnedthrough linelS, -p-ump 19 and line,`

20 while the bottoms from primary settler 17 are returned7 to thereactor throughV line '21. The fresh acid andv rer`` `Another object ofthe invention is to provide an alkylacycle acid enter the reactorthrough pipe 22, Y Hydrocarbons supplied through lines 9 and 10 comIbined with recycled'isobutane fare mixed in the reactor.Y

with the acid catalyst introduced through pipel 22.

Alkylation of the isoparatinic hydrocarbons by the? olefinieVhydrocarbons takes place in the reactor while the mixture is lbeingrapidly circulated and agitatedv by peller 3. which, assures mixing of,the hwlwgefbas: and acidcatalyst. ,y Y Y A f The euent mixture cf.hrdrecarbcns .and actlis discharged fromv thereatcrA through. Pine,first to the primanfl aiisettler, 17. Where t p.f;mft.d t0 Separate intoa hrdroarbvn, Phase and, 219i Phase The acid phase is withdrawn fromthebottom andfis either returned'to the reactor through pipes 21Y and 2? ordiverted throughV pipes 2'4 and 25 to the acid'regen-l` erator 26.Valves are interposed in'these lines to govern the amount of acidreturned to the reactor and L to the regenerator.

The hydrocarbon phase separated in primary settler 17 is discharged fromthe top through pipe 27 into final acid settler 28. In the finalsettler,the'eiuent mixture of hydrocarbons is permitted to separate fromwhatever acid remains, approximately one percent by weight remaining inthe hydrocarbon phase material, the acid bottomsY being withdrawnthrough a discharge line 28a connected into the acid discharge pipe 25through which the acid bottoms from the primary acid settler ow to theacid regenerator 26. The acid bottoms from settlers 17 and 28 passthrough lines 24 and 25 to acid regenerator 28 which is equipped withheating coil 29. A preheater 30 is interposed in pipe 25 ahead of theregenerator. Input and discharge fluid lines 31 and 32 serve tocirculate a heating medium through coil 29 in the bottom of the acidregenerator 26. Regenerated acid passes from the top of regenerator 26through line 33, and after condensation at 34 is delivered through pipe35 into acid accumulator 16. By-pass flow-line 36, controlled by valve37 may be used to by-pass the regenerator 26 or divert a portion of theacid bottoms from the settlers 17 and 28 to accumulator 16. Aspreviously suggested, acid from the accumulator 16 is returned throughlines 18 and 20 to the reactor. Sludge and tars are removed from thebottom of the regenerator 26 through line 38 to suitable disposal.

Hydrocarbon phase eluent The hydrocarbon phase efuent from the acidsettling stage taken of through line 39 contains approximately 0.5 to1.5 percent by Weight of hydrogen fluoride, only a small portion ofwhich is in solution and the balance free acid. If this material werepassed directly to deistobutanizer 53, there would be a severe corrosionproblem occasioned by the free acid at elevated temperature. Likewise,if a neutralization step were imposed between the acid settling stageand the deisobutanizer'tower 53, there would be a severe neutralizationproblem. If an alloy stripper were interposed directly between the finalacid settler and the deisobutanizer, there would be the expense of thisequipment and, additionally, there would be no benet derived in the wayof eliluent refrigeration from the hydrocarbon phase. templates threealternatives.

In the rst alternative, the entire hydrocarbon phase 'effluent is passedthrough line 39b, pressure reduced at valve 40a and fromy thence passedat greatly increased velocity into etluent flash drum 43. Recycle ofliquid through line 47, line 41, distributing head 5, tube bundle 4 andline 42 must be carried out until a ash vaporization equilibrium isreached in the vapor withdrawal step The instant method conquired.

(at the existing temperatures and pressures) within ash drum 43 at whichat least substantially all of the hydrogen fluoride carried over in thehydrocarbon phase is vaporized. As the equilibrium constants of thehydrogen uoride and the hydrocarbon phase efliuent are quite different,this is feasible. At typical conditions of temperature and pressure, theash equilibrium constants for eluent hydrocarbons and hydrogen fluorideare as follows:

l K values at 45 F.

Mole percent: and 26.91 p.s.i.a.

4.56 C33.129 61.58 ic,1.1oo 15.77 no4-.72s

8.06 C,(p1us).oo45 3.03 H12-40.6.00

' uoride out.

265. Also see Industrial and Engineering Chemistry of February 1946.

Eductor 49 would be omitted in such a process with a simple connectionbetween lines 47 and 41. Circulation of liquid through the cooling tubes4 in such case is eiected by the gas lift effect of the vapors evolvedwithin the tubes. It is absolutely necessary that the drum 43, lines 47and 42, and tube bundle 4 be so sized and of such heat exchangingVcapacity relative a given reaction step that such flash vaporizationequilibrium may be achieved. v

The second modification of the invention contemplates the passage of aportion of the total hydrocarbon phase euent from the acid settler 28through line 39h to effluent ash drum 43 after pressure reduction at 40awith suicient total hydrocarbon phase eluent, both liquid and vaporwithout separation, passed through line 39a, pressure reducing valve 40,line 41, distributing head 5, tube bundle 4 and line 42 to provide aflash vaporization equilibrium in the vapor withdrawal step at 43 atwhich at least substantially all hydrogen fluoride is vaporized. If aninsufficient amount of hydrocarbon phase efliuent is passed through line39a to provide such equilibrium through tube bundle heat exchange,recycle of liquid from trap 43 through lines 47 and 42 through the tubebundle 4 and distributing head may be required to achieve the criticalflash vaporization equilibrium. Such liquid will be educted as at 49 bythe high velocity ow from line 41. The function of the eductor 49 is toutilize the energy of the high velocity stream of uid passing throughline 41 after pressure reduction at valve 40. This stream ofhydrocarbons flowing at high velocity draws into pipe 41 liquid from theflash drum 43 through pipe 47.

The third modification of the inventive process contemplates the passageof the entire hydrocarbon phase effluent, including both liquid andvapor without separation, through line 39a, valve 40, line 41, andthrough the distributing head 5 and tube bundle 4 and line 42 into flashdrum 43 whereby to achieve the critical flash vaporization equilibriumwith substantially allhydrogen It is contemplated that, in such case,the recycle through lines 47 and 42 will be but rarely re- If theequilibrium is not reached, however, such recycle is employed preferablywith eduction'at 49.

Back pressure valves 40 and 40a are designed to hold sucient backpressure on the reactor-settler system to prevent appreciableevaporation of the hydrocarbon components contained therein. A liquidlevel control 44 manipulating the valve 45 regulates the discharge ofliquid from the efiluent flash drum 43 through pipe 46.`

Although hydrofluoric acid alkylation is usually carried out in therange of to 100 F., in a system wherein a small amount of propane `isalso present andthe reaction temperature is controlled at about 33 F. to55 F., the back pressure maintained on the settler by valve 1 40 will bein the order of 40 p.s.i.g. to 100 p.s.i.g. Upon passing pressurereduction valve 40 or 40a, pressure upon the hydrocarbon passing intothe cooling elements is reduced to the order of 0 p.s.i.g. to l0p.s.i.g., causing a considerable portion of the lighter components ofthe efliuent to vaporize, resulting in the cooling of the entirehydrocarbon phase. Depending upon the pressure established within thecooling elements of tube bundle of the reactor, the temperature of thehydrocarbon efiiuent phase will be reduced to a gure normally within therange of 15 F. to 30 F. by evaporative cooling, making it suit, able foruse as the cooling medium for the reaction.

The liquid withdrawn from the effluent flash drum 43 through pipe 46 isreturned by pump 50 and pipe 51 to heat exchanger 12'where it is broughtin heat exchange relation with the incoming feed stock supplied throughpipe 14. From the heat exchanger, the liquid passes through line 51 andpreheater 52 to deisobutanizer 53 where the isobutane is taken offoverhead through pipe .54, passed through condenser 55 and thecondensate collected in receiver S6. Condensate accumulated in receiver56 may be either returned to the tower 53 by pump 57 and pipe 53 orreturned in whole or in part by pump 57 and pipe 13 as isobutanerecycle. The alkylate product is recovered from the bottom of tower 53passing off through line 59 to defluorinator 60, thence to conventionaldeisobutanizer and rerun towers not shown.

The vapors separated from the hydrocarbon effluent in the flash drum i3pass off through line 61 to condenser 62 after which the condensate iscollected in effluent flash accumulator 63. Condensate in accumulator 63is recycled to feed pipe 14 through pipe 64, pump 65 and pipe 66.

The effluent flash drum 43 is operated at a pressure in the order of lto 25 p.s.i.a. when the reactor is held at 50 F. The vapors leavingflash drum 43 pass to condenser 62 and accumulator 63 which are operatedat approximately the same pressure.

Cooling medium at the condenser 62 is provided by a closed cyclerefrigeration system such as, for example, one utilizing Freon 12 orpropane. This refrigeration system includes heat transfer coil 62a incondenser 62, connected to compressor 68 by line 67, a line 69 leadingfrom the compressor 68 to a condenser 70 and pipe 71 connecting thecondenser to receiver' 72. A pipe 71 completes the closedcycleconnecting receiver 72 with transfer coil 62a. This refrigeration systemis operated to provide a condensing temperature in the order of 15 F. itwill be noted that the refrigeration system is operated as a closedcycle so that none of the refrigerant comes in Contact with thehydrocarbons being processed or the hydrogen fluoride catalyst. Evenmore important, none of the hydrogen fluoride comes in contact with thecompressor.

By means of this refrigeration system eflluent vapors withdrawn fromflash drum 413 are condensed and their temperature is reducedcommensurate with the temperatures of the circulating refrigerant.vUnder normal operating conditions condensate collected in accumulator 63will have a temperature of approximately 15 to 25 F. The quantity ofisobutane in this condensate stream recycled through pipe 66 willnormally be in the order of 4 to 7 parts by volume for each part ofolefin in the fresh feed. The overhead from the deisobutanizer 53 canthus be reduced by this same amount for any given condition of fixedquality and rerun yield of alkylate, or it follows if the deisobutanizer53 remains fixed, the concentration of isobutane in the reactor isconsiderably increased by the condensed vapors from this source,resulting in increased quality and yield of alkylate.

Although the invention has been described in connection withhydroliuoric acid alkylation with reactor ternperatures in the order of50 F., it should be understood that the reactor may be operated at moreelevated temt eratures since in many cases allcylation units areoperated with reactor temperatures of (S0-70 F. or even as high as 100F. in such cases, the eiiluent flash drum can be operated at highertemperatures and pressures and still provide satisfactory temperaturedifference between the refrigerating medium and chilled eluent. For thetransfer of heat in such cases the closed cycle refrigeration system canalso be operated at ,higher pressures and still provide satisfactorycooling medium for the flash vapor condenser.

Thus it will be seen that the invention is one well adapted to attainall of the ends and objects hereinabove set forth together with otheradvantages which are obvious and which are inherent to the process.

It will be understood that certain features and sub- 70 combinations areof utility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterhereinabove set forth or shown in the accompanying drawings are to beinterpreted as illustrative and not in a limiting sense.

Having thus described my invention, I claim:

l. A process of alkylating isoparafrinic hydrocarbons with olefinichydrocarbons employing hydrogen fluoride as a catalyst, comprising thesteps of contacting iso paraflinic hydrocarbons and olefinichydrocarbons with liquid hydrogen fluoride catalyst in a reaction step,with drawing a mixture of hydrocarbons with hydrogen fluoride catalystas eiluent from said reaction step, separating said effluent into ahydrogen fluoride contaminated hydrocarbon phase and an acid phase in afirst separating step, said reaction step and first separating stepmaintained under sufficient pressure to maintain the hydrocarbons inliquid fo-rm, reducing the pressure on the hydrogen fluoridecontaminated hydrocarbon phase from said first separating step in anevaporative cooling step, passing the pressure reduced hydrogen fluoridecontaminated hydrocarbon phase to a relatively low 'temperature and lowpressure vapor withdrawal step, and passing at least a sufficientquantity of some portion of said hydrocarbon phase after pressurereduction thereof in indirect heat exchanging relationship with saidreaction step to maintain a temperature level in the said vaporwithdrawal step adequate to there establish a flash vaporizationequilibrium at which at least substantially all hydrogen fluoride isvaporized from all liquid in the said vapor withdrawal step, and passinghydrogen fluoride-free liquid from the vapor withdrawal step directly toat least one fractionation step for separation of isoparafilnichydrocarbons from said liquid.

2. A process of alkylating isoparaiiinic hydrocarbons with olefinichydrocarbons employing hydrogen fluoride as a catalyst comprising thesteps of contacting isoparaflinic hydrocarbons and oleiinic hydrocarbonswith liquid hydrogen fluoride catalyst in a reaction step, Withdrawing amixture of hydrocarbons with hydrogen fluoride catalyst as effluent fromsaid reaction step, separating said eilluent into a hydrogen fluoridecontaminated hydrocarbon phase and an acid phase in a first separatingstep,

said reaction step and first separating step maintained' fluoridevaporized from the liquid in the vapor withdrawal step by transferring asuflicient quantity of heat to the hydrocarbon phase er'liuent from thereaction step before removal thereof from the Vapor Withdrawal step toraise the temperature thereof to said flash vaporization equilibriumlevel, by passing at least a portion of said hydrocarbon phase efiluentin indirect heat exchanging relationship with the reaction step andpassing hydrogen fluoridefree liquid from the vapor withdrawal stepdirectly to at least one fractionation step for separation ofisoparafiinic hydrocarbons from said liquid.

References Cited in the file of this patent UNITED STATES PATENTS2,429,205 Jenny et al. Oct. 21, 1947 2,536,515 Penick Jan. 2, 19512,664,452 Putney Dec. 29, 1953

1. A PROCESS OF ALKYLATING ISOPARARRINIC HYDROCARBONS WITH OLEFINICHYDROCARBONS EMPLOYING HYDROGEN FLUORIDE AS A CATALYST COMPRISING THESTEPS OF CONTACTING ISOPARAFFINIC HYDROCARBONS AND OLEFINIC HYDROCARBONSWITH LIQUID HYDROGEN FLUORIDE CATALYST IN A REACTION STEP, WITHDRAWING AMIXTURE OF HYDROCARBON WITH HYDROGEN FLUORIDE CATALYST AS EFFIUENT FROMSAID REACTION STEP, SEPERATING SAID EFFLUENT INTO A HYDROGEN FLUORIDECONTAMINATED HYDROCARBON PHASE AND AN ACID PHASE IN A FIRST SEPARATINGSTEP, SAID REACTION STEP AND FIRST SEPERATING STEP MAINTAINED UNDERSUFFICIENT PRESSURE TO MAINTAIN THE HYDROCARBONS IN LIQUID FORM,REDUCING THE PRESSURE ON THE HYDROCARBONS FLUORIDE CONTAMINATEDHYDROCARBON PHASE FROM SAID FIRST SEPARATING STEP IN AN EVAPORATIVECOOLING STEP, PASSING THE PRESSURE REDUCED HYDROGEN FLUORIDECONTAMINATED HYDROCARBON PHASE TO A RELATIVELY LOW TEMPERATIVE AND LOWPRESSURE VAPOR WITHDRAWAL STEP, AND PASSING AT LEAST A SUFFICIENTQUANTITY OF SOME PORTION OF SAID HYDROCARBON PHASE AFTER PRESSUREREDUCTION THEREOF IN INDIRECT HEAT EXCHANGING RELATIONSHIP WITH SAIDREACTION STEP TO MAINTAIN A TEMPERATURE LEVEL IN THE SAID VAPORWITHDRAWAL STEP ADEQUATE TO THERE ESTABLISH A FLASH VAPORIZATIONEQUILIBRIUM AT WHICH AT LEAST SUBSTANTIALLY ALL HYDROGEN FLUORIDE ISVAPORIZED FROM ALL LIQUID IN THE SAID VAPOR WITHDRAWAL STEP, AND PASSINGHYDROGEN FLUORIDE-FREE LIQUID FROM THE VAPOR WITHDRAWAL STEP DIRECTLY TOAT LEAST ONE FRACTIONATION STEP FOR SEPERATION OF ISOPARAFFINICHYDROCARBONS FROM SAID LIQUID.